Positive column lamp



Jan. 18, 1949. a LEMMERS 2,459,567

POSITIVE COLUMN LAMP Filed Dec. 21, 1946 Inven'l'ri v Eugene Lemmer-s,

by MW His 'ATTcr-neij.

Patented Jan. 18, 1949 POSITIVE COLULIN LAMP Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application December 21, 1946, Serial No. 717,719

My invention relates to gaseous electric discharge lamps, and more particularly to lamps of the positive column type.

An object of my invention is to provide a posiused for various special applications where the approximately half wave operation flicker is not objectionable, such as in long-wave ultraviolet applications. Further objects and advantagesof my invention will appear from the followin description and from the drawing.

The lamp more specifically described hereinafter is a positive column, half wave or D. C. type having only one cathode and one anode, rather than a pair of electrodes which function alternately as cathode and anode. The anode is constructed to be unable to pass any, or at least very low, currents when connected as cathode on the voltages supplied for operating the lamp on alternating current.

By mounting the cathode and anode on a single stem and having all the lead-in wires at one end, instead of at both ends as is usual for a positive column lamp, savings in mounting andsealing are made. Single-ended positive column lamps have been made, but they have had to have the, leads to the far end of the envelope insulated. This is costly and fraught with difliculties. These difliculties havebeen obviated and the insulation eliminated by using one cathode and an anode, as mentioned above, and locating the cathode at the far end of the envelope, that is. the end remote from that in which the leads are sealed. If these positions are reversed a positive column discharge will not be formed. It is also necessary that the lamp be designed to have a starting and operating voltage gradient which is below a limiting value which would force the anode and lead wires to conduct an appreciable amount of current as a cathode. In other words the structure can be made too long for successful operation. However, althou h particular values are -set forth in a specific example described hereinafter, it is not possible to set forth definite general values, as will be appreciated by those skilled in the art, since they depend on a number of variables which may be readily determined for lamps of diflferent capacity. Thus. the lamp voltage is dependent upon the length and diameter of the envelope. the type of gaseous atmosphere and its pressure, and current density. The maximum envelope length is determined by its diameter (greater for envelopes of greater diameter), the operating current (greater length permissible for greater current), and the electron-emissive characteristics of the anode and lead wire materials. The latter characteristic is most favorably controlled by using graphite or carbon for the anode, or by applying soot or carbon to a metal anode and leads.

For a further understanding of my invention. reference may be had to the drawing which is an elevation of a' lamp comprising my invention, together with an operating circuit diagram.

Referring to Fig. 1, the lamp comprises a tubular envelope l of vitreous material. When the lamp is to be used as a source of germicidal radiations of 2537A wavelength the said envelope is made of a special glass which transmits those radiations, such as that marketed as #9741 bythe Coming Glass Works, of Corning,'New York. Alternatively, the inner surface of the envelope may be coated with a phosphor such as, for example, calcium tungstate or the cerium-activated calcium phosphate disclosed and claimed in the Roberts Patent 2,306,567 which convert the radiations of 2537A generated in a mercury vapor discharge to ultraviolet radiations oi longer wavelength.

The end of the envelope I is closed by a stem 2 through which are hermetically sealed the lead-in wires 3, l and 5. The lead '3 carries an anode 6 adjacent the stem 2, while the leads 4 and S extend longitudinally of the envelope to its opposite end where they support an activated thermionic cathode I. The said leads may be made of any suitable metal such as, for example, an alloy of iron, nickel and cobalt known as Fernico, and it will be noted that they are bare, that is, devoid of insulation; the said leads 4 and 5 being exposed directly to the positive column 3 formed between the cathode 1 and anode 6 and defined by the walls of the envelope l.

The anode 6 is made of a material selected for its non-electron-emissive properties, i. e., it has a high work function. By far the best material known to me to be satisfactory for this purpose is carbon or graphite. However, instead of a solid disc or block of carbon, I may use a metal anode coated with soot or carbon. An anode of bare metal such as iron, for example, is not suitable. The cathode l, on the other hand, is made highly electron-emissive, as by coating a suitable base metal with alkaline earth oxides like barium and strontium oxides. A suitable form consists of a coiled or coiled-coilstructure of tungsten wire overwound with finer tungsten wire and impregnated with alkaline earth oxides, as disclosed and claimed in the Aicher Patent 2,306,925.

The envelope I contains a suitable ionizable atmosphere at a pressure of a few millimeters of mercury. A suitable atmosphere is argon at a pressure of about 1-l0 mm. together with a small quantity of mercury which, during operation of the lamp, attains a pressure of a few microns, for example about ten microns.

As illustrated in Fig, 1, the lamp may be operated from a leakage reactance auto-transformer 3 connected to the terminals 9, in of a source of alternating current, the transformer secondary being connected to the cathode lead t and anode lead 3, If desired, the cathode may be separately heated by connecting its leads d and ii across a separate source of potential, as by tapping into the transformer d, in which case a switch may be provided in the circuit to lead 5 whereby to preheat the cathode only during starting the lamp.

The following data is given as an example of specific details illustrating, but not limiting, an embodiment of the invention: An envelope of inch diameter with a gap of about to mm. between the cathode l and anode d; a filling of 6 mm. of argon plus a drop of mercury; a transformer 8 connected to a 118 volt, 60 cycle alternating current source 9, id and having an open circuit voltage of 180 volts; the potential drop across the cathode l and anode 6, during operation, being between 16 and 30 volts with a current consumption of 200 milliamperes.

In a lamp proportioned as thus .described and as shown in the drawing, a potential of about 80-100 volts is necessary to sustain a discharge between the lead 4 and anode B so that the are voltage of 16-30 is sufficiently well below that value to insure successful operation of a positive column discharge from cathode 1 to anode 6, rather than a discharge from lead 4 to anode 6. Obviously, the reverse would happen if the arc voltage were raised to a value in the neighborhood of 80 volts in this case, as by unduly lengthening the arc gap, constricting the envelope diameter, raising the gas pressure, or lowering the current density.

While I prefer to employ two cathode leads 4 and 5 in order to permit activation of the cathode by passing current directly therethrough, one of the leads (5) might be omitted and the cathode heated for activation by a high frequency coil as well known in the art. .Also, when employing both leads 4 and 5 they may be twisted together or otherwise connected together outside the envelope l to short circuit the cathode 1. Furthermore, the lamp may be made a full-wave rectifying type by employing two anodes 6 arranged side-by-side in the lower end of the envelope.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A positive column gaseous electric discharge lamp comprising a sealed tubular envelope the walls of which define the discharge path, an ionizable gaseous atmosphere in said envelope at a pressure of a few millimeters of mercury, an anode having a work function not materially lower than that of carbon and an activated thermionic cathode at opposite ends of said envelope, a plurality of lead-in conductors hermetically sealed through the end of said envelope adjacent said anode, one of said conductors extending to said anode and another of said conductors extending the length of the positive column to said cathode, said last mentioned cathode conductor being of bare metal exposed to the positive column, the lamp being proportioned to have a voltage gradient below a limiting value at which the anode and lead-in conductors would conduct an appreciable amount of current as a. cathode.

2. A positive column gaseous electric discharge lamp comprising a sealed tubular envelope the walls of which define the discharge path, an ionizable gaseous atmosphere in said envelope at a pressure of a few millimeters of mercury, an anode having a work function not materially lower than that of carbon and an activated thermionic cathode at opposite ends of said envelope, a plurality of lead-in conductors hermetically sealed through the end of said envelope adjacent said anode, one of said conductors extending to said anode and a pair of said conductors extending the length of the positive column to respective ends of said cathode, said pair of cathode conductors being of bare metal exposed to the positive column, the lamp being proportioned to have a voltage gradient below a limiting value at which the anode and lead-in conductors would conduct an appreciable amount of current as a cathode.

3. A positive column gaseous electric discharge lamp comprising a sealed tubular envelope the walls of which define the discharge path, an ionizable gaseous atmosphere in said envelope at a pressure of a few millimeters of mercury, an anode and an activated thermionic cathode at opposite ends of said envelope, said anode being composed, at least on its surface, of carbon, a plurality of lead-in conductors hermetically sealed through the end of said envelope adjacent said anode, one of said conductors extending to said anode and a pair of said conductors extending the length of the positive column to respective ends of said cathode, said pair of cathode conductors being of bare metal exposed to the positive column, the lamp being proportioned to have a voltage gradient below a limiting value at which the anode and lead-in conductors would conduct an appreciable amount of current as a cathode. 1

4. In combination, a, positive column gaseous electric discharge lamp comprising a sealed tubular envelope the walls of which define the discharge path, an ionizable gaseous atmosphere in said envelope at a pressure of a few millimeters of mercury, an anode having a work function not materially lower than that of carbon and an activated thermionic cathode at opposite ends of said envelope, a plurality of lead-in conductors hermetically sealed through the end of said envelope adiacent said anode, one of said conductors extending to said anode and a pair of said conductors extending the length of the positive column to respective ends of said cathode, said pair of cathode conductors being of REFERENCES CITED bare metal exposed to the positive column, and The l W n8 references are of record in the means to supply an alternating current operatfile of this Patent: in: potential across said cathode and anode in- 5 m eluding means to limit the current thereto, the UN STATES PATENTS la'mp being proportioned in correlation with the Number Name Date current limiting means to have a voltage gradient 2,009,221 Bmunes July 23, 1935 below a limiting value at which the anode and 2,030,399 Rompe 11, 1986 lead-in conductors would conduct an appreciable, 10 21103378 Holst 21, 1937 amount of current as cathode. 2,329'126 Lemme Sept- 1943 2,341,990 Inman Feb. 15, 1944 EUGENE LEMMERS. 2,420,942 Foulke May 20, 194': 

